1. Field of the Invention
The present invention relates to apparatus and methods for controlling the direction of drilling of a borehole in a well and more particularly to a steering system for directing three dimensionally the drilling of a bit and still more particularly to a steering assembly with electric power from the surface and communication to and from the surface and which can change bend angle and the direction while drilling.
2. Background of the Invention
The conventional practice for drilling a borehole in a well in a controlled direction requires multiple mechanisms to control the direction while drilling. A common prior art tool for controlling the direction of drilling is a bottom hole assembly consisting of the drill bit, stabilizers, drill collars, heavy weight pipe, and a positive displacement motor (mud motor) having a bent housing. The bottom hole assembly is connected to a drill string or drill pipe extending to the surface. The assembly steers by sliding (not rotating) the assembly with the bend in the bent housing in a specific direction to cause a change in the borehole direction. The assembly and drill string are rotated to drill straight.
Another type of prior art tool steers using non-rotating stabilizers, located some distance above the drill bit, to push radially against the side of the borehole with a force, usually constant, so that the bit will drill in the opposite direction at a controlled rate while drilling ahead so that the direction of the hole is altered. This type of steering tool can change direction at a maximum rate of about fifteen degrees per hundred feet of hole drilled and must be run with a rotary drill string or below a mud motor. One such system uses valves and hydraulic fluid to extend adjustable blades engaging the borehole wall to change direction.
Still another prior art steering tool steers using paddles located some distance above the bit. The paddles push off the side of the borehole in a specific direction as the bottom hole assembly rotates in the hole in order to alter the direction of the borehole. This type of steering tool can change direction at a maximum rate of about ten degrees per hundred feet of hole drilled and must be run with a rotary drill string or below a mud motor.
A further prior art steering tool includes a housing with a ball joint and adjustable blades adjacent the ball joint and bit whereby the extension of the blades causes the downhole portion of the housing to bend at the ball joint with respect to the remainder of the bottom hole assembly. Steerable systems, which contact the wall of the borehole to change bend angle or direction, create an undesirable drag against the borehole wall while drilling. This requires additional drilling force on the bit to overcome this drag. Such contact also inhibits the sliding of the bottom hole assembly within the borehole while drilling.
Another method includes a steerable system having wedges, which are actuated by a pressure differential extending the length of the drill string, against cams to drive them out to change drilling direction. Drilling must be stopped to change drilling angle.
The prior art also includes electrically controlled bent subs. These, however, only control the bend in one plane of the tool. Further, the prior art electrically controlled bent subs can not control the direction of the bend without rotating the drill string.
Although various prior art steerable systems can vary bend angle downhole, few can vary both bend angle and direction. None of the prior art tools control both the angle of the bend and the direction of the bend while drilling. Often it is necessary to pull the entire bottom hole assembly out of the hole to change the angle or the direction of the bend.
There are prior art systems which provide electrical power and hydraulics from the surface using an umbilical mounted on the outside of steel coiled tubing. However, such systems do not provide power to the downhole tool directly from the surface through the wall of the coiled tubing.
The present invention overcomes the deficiencies of the prior art.